1. Field of the Invention
This invention relates to biodegradable polymers and articles manufactured therefrom, which polymers include a microbe-inhibiting agent.
2. Description of the Related Art
Degradable polymers have found applications in diverse areas such as garbage bags, golf tees, food containers, foamed packing materials, chewing articles for pets, and even writing pens. Degradable polymers can be chosen for an application for many different reasons, including their tendency to break down under appropriate biological or disposal conditions, their ability to serve as a digestible or otherwise harmless mastication material for people or animals, or for public relations purposes.
A common class of biodegradable polymers is starch-based. Pure starch polymers do not possess the desired properties for most applications, as they are brittle and are unduly affected by moisture. They are therefore commonly blended and/or reacted with other polymers. U.S. Pat. No. 5,321,064 discloses a class of biodegradable polymers in which starch is reacted with synthetic polymeric material such as polyethylene, polystyrene, polypropylene and polyvinyl chloride. U.S. Pat. No. 5,409,973 discloses a class of materials based on starch and an ethylene copolymer. U.S. Pat. No. 5,360,830 discloses a similar material produced in expanded form. U.S. Pat. No. 5,459,258 discloses a class of biodegradable materials based on the combination of hydrophobic polysaccharides, one thermoplastic and the other non-thermoplastic.
Biodegradable starch-based resins are available commercially from a number of manufacturers, such as Starchtech(trademark) and Novamont(trademark). Starchtech(trademark) sells a series of such polymers under the xe2x80x9cRe-NEW(trademark)xe2x80x9d trade name. Novamont(trademark) offers several classes of such polymers under the trade name, xe2x80x9cMater-Bi(trademark).xe2x80x9d
Biodegradable poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) resins, as well as PLA-PGA copolymers have numerous desirable properties. (See: Ratner, B D et al., Eds., Biomaterials Science, Academic Press, New York, 1996, p. 64; Naitove, M., Plastics Technology, March 1995, p. 15.) A variety of commercial grades are available from Cargill, under the name xe2x80x9cEcoPLA(trademark),xe2x80x9d and also from various biomedical suppliers. Adjustment of the PGA:PLA ratio in a material can be used to fine-tune the texture, degree of hydrophilicity and rate of biodegradation. For example, PGA is more hydrophilic than PLA, so that increasing the PGA content will increase the hygroscopic property (uptake of water, saliva, or any other fluid). In addition, although PGA is highly crystalline, which generally slows its degradation, it becomes markedly less crystalline, and more degradable, when blended with PLA.
Materials based on polyhydroxybutyrate (PHB) are also attractive. One example, available commercially under the name Biopol(trademark) comprises a blend with 3-hydroxyvaleric acid (PHV). PHB is generally highly crystalline, inflexible, and difficult to process. Blending with PHV diminishes the crystallinity, resulting in more flexible, more easily processed materials.
Polycaprolactone, either pure or blended with other materials, is a generally attractive degradable material that has found uses in medical applications such as sealing materials for wounds.
Other attractive degradable materials include, the poly(amino acids), the polyanhydrides, poly (ortho esters), and polyphosphazenes.
The mechanism by which the materials of interest are degraded typically involves the metabolic or digestive action of microbes or enzymes generally derived from those microbes breaking down the molecular structure or catalyzing the hydrolysis of the materials. In many cases, however, significant hydrolysis occurs in the absence of direct microbial or enzymatic action.
The deliberate exposure of degradable materials to microbial or digestive conditions, such as in composting or mastication, is expected to bring about their relatively rapid degradation. Unfortunately, however, such materials are naturally susceptible to microbial action over their entire lifetime. Articles constructed from biodegradable materials therefore may support microbial growth long before they are degraded or otherwise consumed. Biodegradable materials often readily absorb water which generally promotes microbial growth. This property may be a serious problem for materials requiring prolonged storage, especially if the storage environment is humid or otherwise encourages growth of fungi or bacteria (e.g., dark, poor ventilation, dirt, etc. ). This is an especially serious problem for materials that are particularly intolerant of microbial proliferation, such as materials designed to contact food. Examples of the latter include plastic cutlery and tableware, plastic or paper/plastic composite cups, plastic or paper/plastic composite food containers, etc. Items the use of which involves contact with warm, dirty, and/or humid conditions are also particularly at risk, such as chewing articles for pets.
U.S. Pat. No. 5,744,516 discloses biodegradable resin molded articles made from biodegradable resin raw material, a biodegradable additive and an additive made of a substance existing in the nature. Also disclosed are (a) injection molded articles made of a biodegradable resin and an anti-biotic substance, and (b) resin molded articles having a layer of a biodegradable resin, and a layer of a photolytic resin covering the resin layer and also containing an antibiotic. This document states that prolonged use of a biodegradable resin requires first that degradation by bacteria be restricted, as by adding an antibiotic to the resin (citing Japanese Unexamined Patent Publication (Kokai) No. 5-51073).
It is often desirable to fine-tune (or even to reduce markedly) the degree of biodegradability of a polymer. For blended or reacted biodegradable polymers, this can be accomplished by altering the proportion of, and/or degree of, reaction with the degree of branching, cross-linking, etc.) can be varied or a protective coating added. These techniques for adjusting the degree of biodegradability, however, suffer from the fact that they often require complex engineering and can have unwanted side effects on useful properties (e.g., strength, impact resistance, processability, UV- or heat-resistance, etc.). There is thus a need for a simple way to alter the degree of biodegradability of a polymer without affecting other desirable properties.
The present invention provides a simple approach to altering the biodegradability of a polymer without affecting other properties and thereby overcomes the shortcoming of the prior art.
The invention provides compositions and methods that incorporate an effective amount of a microbe-inhibiting (MI) compound or cocktail of compounds (all of which are referred to herein interchangeably as xe2x80x9ccompoundxe2x80x9d or xe2x80x9cagentxe2x80x9d) into a biodegradable polymer, most preferably, starch-based polymers. The starch can be complexed with synthetic organic polymeric materials such as polyethylene, polypropylene and copolymers of ethylene and propylene. The synthetic polymers are preferably linked to the starch by organic linkers such as maleic anhydride. Such polymers linkers are described in U.S. Pat. 5,321,064, which is incorporated herein by reference. This patent discloses a class of biodegradable polymers in which starch is reacted with synthetic polymeric material such as polyethylene. Although post-incorporation of the agent can be effective (e.g., via soaking or high-pressure impregnation), it is preferred to incorporate the agent into the structure of the polymer at the time of compounding or at the time of formation (e.g., molding) of the final polymer article.
According to one embodiment of the invention, a formed body in the shape of a useful article comprises a biodegradable polymer composition including a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles. The microbe-inhibiting compound or compounds are selected from the group consisting of diiodomethyl-p-tolylsulphone; 2,4,4xe2x80x2-trichloro-2-hydroxydiphenylether; 10,10-oxy-bis-phenoxarsin; N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide; a zinc complex of pyrithiione termed zinc omadine; silver hydroxyapatite: 2-N-octyl-4-isothiazolin-3-one; copper-bis-(8-hydroxyquinolline); N-(trichloromethyl-thio)phthalimide; and natural microbe-inhibiting compounds.
In one embodiment, the polymer composition comprises starch.
In another embodiment, the formed body is a foamed container. In a preferred embodiment, the formed body is a loose fill packing pellet.
Further according to the invention, a foamed body in the shape of a useful article comprises a biodegradable polymer composition including a matrix polymer containing a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles, wherein the microbe-inhibiting compound or compounds are inhibiting to at least two classes of microbial agents selected form fungi, bacteria, algae, protozoa and microscopic parasitic organisms. In one embodiment, the polymer composition comprises starch. In another embodiment, the foamed body is a foamed container. In another embodiment, the foamed body is a loose fill packing pellet.
Still further according to the invention, a foamed body formed in the shape of a useful article comprises a biodegradable polymer composition comprising a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound that inhibits the growth of microbes in or on the articles, wherein the microbe-inhibiting compound is a cocktail of anti-microbial agents and where the polymer composition is formed into a foamed body. In one embodiment, the polymer composition comprises starch. In another embodiment, the foamed body is a foamed container. In yet another embodiment, the foamed body is a loose fill packing pellet.
Still further according to the invention, an organic polymer composition for forming useful articles comprises a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound that inhibits the growth of microbes in or an the articles and the microbe-inhibiting compound is a cocktail of anti-microbial agents. The organic polymer is selected from the group consisting of polyethylene, polypropylene, polystyrene and polyvinyl chloride In one embodiment, a useful article, such as a food contacting body, is formed from organic polymer composition and preferably is foamed.
Still further according to the invention, an organic polymer composition for forming useful articles comprises a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound that inhibits the growth of microbes in or on the articles. The microbe-inhibiting compound is a cocktail of anti-microbial agents and the polymer composition is a polymer blend.
Still further according to the invention, an organic polymer composition for forming useful articles comprises a matrix polymer containing a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles. The microbe-inhibiting compound or compounds are inhibiting to at least two classes of microbial agents selected from fungi, bacteria, algae, protozoa and microscopic parasitic organisms. Further, the organic polymer comprises a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene and polyvinyl chloride.
In one embodiment, a foamed body in the form of a useful article is made from this organic polymer composition. Preferably, the foamed body is a food-contacting body.
Still further according to the invention an organic polymer composition for forming useful articles comprises a matrix polymer containing a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles. wherein the microbe-inhibiting compound or compounds are inhibiting to at least two classes of microbial agents selected from fungi, bacteria, algae, protozoa and microscopic parasitic organisms and wherein the polymer composition is a polymer blend.
Still further according to the invention a biodegradable polymer composition for forming useful articles comprises a host polymer that has incorporated therein an effective amount of a microbe-inhibiting compound or compounds which inhibit the growth of microbes in or on the useful articles. The microbe-inhibiting compound or compounds are selected from the group consisting of diiodomethyl-p-tolylsulphone; 2,4,4xe2x80x2-trichloro-2-hydroxydiphenylether; 10,10-oxy-bis-phenouarsin; N-trichloromethylthio -4-cyclohexene-1,2-dicarboximide; a zinc complex of pyrithiione termed zinc omadine; silver hydroxyapatite; 2-N-octyl-4-isothiazolin-3-one; copper-bis -(8-hydroxyquinolline); N-(trichloromethyl-thio)phthallmide; and natural microbe-inhibiting compounds, and the polymer is selected from the group consisting of polyethylene, polypropylene, polystyrene and polyvinyl chloride.
In one embodiment, a foamed body in the form of a useful article is made from this biodegradable polymer composition. Preferably, the foamed body is a food-contacting body.
Desirable MI agents can be obtained in various forms, e.g., as a relatively pure powder, a liquid concentrate, in a resin carrier where the carrier is one of the components of a desired blend.
For the most part, the preferred MI compounds or cocktails of compounds are effective against a broad range of microbes, particularly fungi and bacteria, and have a number of other desirable properties, including: safe at and above the concentrations required for use; degradation temperatures appreciably higher than the typical processing temperatures of the desired host plastics; when interacting with host plastic, do not lower their own degradation temperature or that of the host plastic; are readily dispersed In the plastic; and readily diffuse in the plastic.
The polymers containing the MI compounds are used to manufacture any of a number of articles, preferably ones that come In contact with foods such as foam containers and fruit shock absorber nets. Also intended are loose fill pellets.
In one embodiment of the invention, a biodegradable organic polymer composition for forming useful articles comprises a host polymer that has incorporated therein an effective amount of a MI compound that inhibits growth of microbes in or on the article formed with the composition during the useful life of the article, thereby retarding degradation of the composition and the article during its useful life. In a preferred embodiment, the host polymer includes starch.
The MI compound preferably has at least one of antifungal and antibacterial activity. The concentration of the MI compound is between about 0.001% and about 3% by weight in the polymer, more preferably between about 0.005% and about 1% by weight.
When the MI compound is In particulate form In the host polymer, the microbe-inhibiting inhibiting compound is in a solid phase at a concentration that is preferably between about 1.5 and about 1000 times the MI compound solid phase minimal inhibitory concentration, more preferably, between about 5 and about 300 times the MI compound solid phase minimal inhibitory concentration (xe2x80x9cMICxe2x80x9d).
When the MI compound is substantially in solution in the host polymer, the microbe-inhibiting compound is preferably at a concentration between about 1 and about 20 times the microbe-inhibiting compound""s solid phase MIC, more preferably, between about 2 and about 20 times the MIC.
In the above composition, the host polymer preferably comprises a synthetic organic polymer, preferably one selected from the group consisting of polyethylene, polypropylene, a copolymer of ethylene and propylene, polystyrene, polyvinyl chloride, polyhydroxybutyrate, polyhydroxybutyrate blended with 3-hydroxyvaleric acid, polycaprolactone, a poly(amino acid), a polyanhydride, a poly (ortho ester), and a polyphosphazene.
When starch is included, it is preferably linked to the synthetic organic polymer by an organic linker group, preferably maleic anhydride.
In the above composition, the MI compound retards degradation partially or completely during storage of the article.
The MI compound above is preferably selected from the group consisting of diiodoethyl-p-tolylsulphone (DIMTS), triclosan, 10,10xe2x80x3-oxy-bis-phenoxarsin)); a tributyltin derivative Intercide(trademark);(N-(trichloro copper-bis-(8-hydroxyquinoline); (N-tri 2-N-octyl-4-isothiazolin-3-one; a zinc complex of pyrithione termed Zinc Omadine; and silver hydroxyapatite. Preferred forms of triclosan are Irgasan DP(trademark) or Ultrafresh NM-100(trademark). The MI compound can be a cocktail of antimicrobial agents as in Bacticlean(trademark)
In a preferred starch-based composition, the synthetic polymer is maleated ethylene-propylene copolymer and the MI compound is DIMTS.
In another embodiment of the invention, an article of manufacture is formed from the biodegradable organic polymer compositions described above. The article can be molded or extruded. Preferably, the article is one which, in its normal use, contacts a food. Thus, the article can be selected from the group consisting of a foam food container or support, a shock absorber net, a loose-fill foam packing pellet, a cutlery or tableware article and a drinking cup. The article can also be selected from the group consisting of a loose-fill foamed packing pellet, a pet chewing article; a garbage bag and a golf tee.
In another embodiment of the invention, a method for retarding the undesired degradation of a biodegradable organic polymer composition that is optionally formed into a useful article comprises incorporating into the polymer an effective amount of a MI compound that inhibits growth of microbes in or on the composition or article. In this method, the polymer composition preferably Includes starch.
Still further according to the invention, a method of rendering a biodegradable organic polymer composition, or a useful article formed therefrom, resistant to microbial invasion, growth, proliferation or spread comprises incorporating into the organic polymer composition, preferably one that includes starch, an effective amount of a MI compound.
In the foregoing method, the MI compound can be in the form of a powder, a liquid concentrate or can be first incorporated or integrated into a resin carrier. Incorporation of the microbe-inhibiting compound into the polymer can be performed at the time of compounding the polymer or at the time of forming the article.
In this method, the MI compound can be in particulate form, wherein the incorporating comprises the steps of dry-mixing, heating and, optionally, further mixing the microbe-inhibiting compound and the polymer. The incorporating can comprise a step of extruding, processing in a mixer or milling in a rolling mill.
In a preferred method, the composition is formed by the steps of mixing: 100 parts of dry starch with 40 parts of maleated ethylene-propylene copolymer, to form a first mixture;
blending the first mixture with 4 parts of a carrier resin comprising 6% MIMTS in ethylene vinyl acetate, to form a second mixture; and
mixing the second mixture in an internal hot mixer for 14 minutes at 180xc2x0 C.